/**
 * 5. 最长回文子串
 * https://leetcode.cn/problems/longest-palindromic-substring/description/
 */
class Solution {
    public String longestPalindrome(String s) {
        int begin = 0, len = 0, n = s.length();
        for (int i = 0; i < n; i++) {
            //1、扩展奇数长度的子串
            int left = i, right = i;
            while (left >= 0 && right < n && s.charAt(left) == s.charAt(right)) {
                left--;
                right++;
            }
            if (right - left - 1 > len) {
                begin = left + 1;
                len = right - left - 1;
            }
            //2、扩展偶数长度的子串
            left = i;
            right = i + 1;
            while (left >= 0 && right < n && s.charAt(left) == s.charAt(right)) {
                left--;
                right++;
            }
            if (right - left - 1 > len) {
                begin = left + 1;
                len = right - left - 1;
            }
        }
        return s.substring(begin, begin + len);
    }
}